The invention relates to a method and circuit arrangement for improving the resolution of digital signals, in particular luminance and/or chrominance TV signals, the sampled values of which are transformed in blocks, for example by discrete cosine transformation, in such a way that one positive coefficient representing a uniform component and several negative and/or positive coefficients representing alternate components are created and are, in the course of calculation, limited to a smaller number of values, rounded off and inversely transformed after transmission and/or storage.
In order to reduce the quantity of data during digital transmission of TV signals, it is known to initially transform the TV signals in blocks from the spatial domain to the frequency domain, then to transmit only those spectral coefficients obtained by means of the transformation which are essential and to zero out the nonessential ones, and finally to inversely transform the transformed values back into the spatial domain. Transformation takes place by a multiplication of the signal values with a transformation function, the number of bits per sample increasing because of multiplication within the transformation. In order to reduce the number of bits per sample, but still having a sufficient resolution of the gradations of the luminance and/or chrominance signal values, for example 8 bits plus sign, a two-times integer division of the coefficient blocks and thus a rounding off of the transformation values is performed in connection with, a two-dimensional transformation for example, of the block size 8.times.8.
Such a technique is described, for example, by G. Bostelmann, et al., in an article entitled "Codierung von Videosignalen [Coding of Video Signals]" in Elektrisches Nachrichtenwesen, Vol. 59, No. 3, 1985, pages 286-294.
It has been shown that with small AC-coefficients of the transformed coefficients, i.e., with smooth patterns of the original picture, coarser patterns appear after inverse transformation. The reason for this is that, because of the rounding off of the transformed values, information is lost and thus is lacking after inverse transformation. This gives rise to visible interference because of a lack of masking by signal components with higher frequencies.